KafkaSQL message that allows custom SQL to be executed

[EricWittmann]

There is currently no way to fix the in-memory H2 database when using the KafkaSQL storage. If some sort of data corruption occurs, it is difficult to fix because the kafka messages are immutable. We should introduce a Kafka message that can contain a custom SQL command that will be executed against the in-memory DB. This way data corruption issues could be fixed by posting such a message to the kafka topic.

[EricWittmann]

• Support SQL statement execution in kafkasql storage #4887

[EricWittmann]

Done.